Road Salt Research

Background

Because of low purchase price and ready accessibility, road salt (sodium chloride) is the most commonly used de-icing chemical, and its use on highways has increased steadily since the 1940s. New York State is the largest user of road salt in North America, and the amount of road salt used in the Adirondack Park greatly exceeds the inputs of other regionally important pollutants like acid deposition. Yet, despite this higher input we know comparatively little about the effects of road salt on Adirondack ecosystems. Road salt has the potential for significant negative effects on forest and aquatic ecosystems that may be on par with or greater than those reported for other regional pollutants. Much research has been done on road salt, and its general effects on forest, soil, and water resources are well documented, but questions remain on the significance of road salt compared to other pollutants, and additionally little research has been done that can be used directly by agencies and municipalities to improve winter road management practices to reduce the environmental impacts of road salting.

Objectives

The objectives of this work are to understand the effects of road salt application rates (tons of salt per km of road) on soil fertility and water quality and to develop practical information to aid agencies and municipalities in selecting management practices that reduce the impacts of road salt on forest and water resources.

Approach

Water quality is being monitored intensively on a network of 15 streams in the Adirondack Park representing a broad range of road salt application rates. The data is being used to develop relationships between road salt application rate and water quality response that managers can then use to help choose and justify alternative road salt application rates to meet water quality objectives. Results are being communicated at meetings, and will be comunicated in journal articles and in a special forum devoted to winter road management. Though the focal region is the Adirondacks, because road salt is widely applied across the Northern Forest region and Adirondack soils and geology are similar to others in the region, the results will be widely applicable.

About 160,000 metric tons of road salt (NaCl) is applied to roads in the Adirondack Park every year, making road salt one of the most significant regional pollutants in terms of annual load. This load delivers 2,740 megamoles of charge as Na ions per year, a large portion of which should enter roadside soils and displace other cations from the exchange complex, which may then leach from the soil and deplete fertility. We assessed the effect of road salt on cation leaching by comparing average Ca, Mg, K, and Na concentrations in lakes in watersheds without paved roads (n=66) to lakes in watersheds with paved roads (n=100), with paved roads being a surrogate for road salt. A simple input-output model was used to estimate annual watershed release for each cation based on lake concentrations and runoff. Median Ca, Mg, and K concentrations in lakes in watersheds with paved roads were double their median concentrations in lakes in watersheds without paved roads. The median Na concentration in lakes in watersheds with paved roads was four times greater than without paved roads. The estimated annual watershed release without paved roads was within the range of values reported for other watersheds in the region for all cations. The estimated annual watershed release of Ca, Mg, and Na was 31% greater with paved roads compared to without paved roads. This difference in watershed release strongly suggests that road salting increases cation loss from soils in the Adirondack Park; this loss is a significant flux that should be accounted for when assessing the impacts of pollutants on biogeochemistry and ecosystem health, not only in the Adirondacks but wherever road salt is applied in the Northern Forest.

The mission of the Adirondack Watershed Institute of Paul Smith's College is to create scientifically-sound knowledge about terrestrial and aquatic ecosystems and human relationships with the environment, enhance the educational opportunities available for undergraduate students and to engage the Adirondack Community in ways that facilitate the stewardship of our natural resources.